create default libraries folder, though not yet used

.travis.yml

@@ -8,6 +8,7 @@ script:
   - wget -O arduino.tar.xz https://www.arduino.cc/download.php?f=/arduino-nightly-linux64.tar.xz
   - tar xf arduino.tar.xz
   - mv arduino-nightly $HOME/arduino_ide
+  - mkdir -p $HOME/Arduino/libraries
   - cd $HOME/arduino_ide/hardware
   - mkdir espressif
   - cd espressif